U.S. officials are working to find out as much as possible about two apparently stolen passports connected with the missing Malaysia Airlines jet that vanished this morning near Vietnam.

Confirmation of the safety of two passengers, one Italian and one Austrian national, whose names appeared on the plane's passenger manifest but were not in fact on board the flight, has added to the mystery surrounding missing Malaysia Airlines Flight MH370, which was carrying 239 people.

The fact that there were apparently two males on board the flight posing as an Austrian and an Italian is tantalizing and suspicious, and could be meaningful, or it could have nothing at all to do with what happened to the plane, sources said.

An Austrian Foreign Ministry press spokesperson confirmed via Twitter today that the Austrian passenger supposedly on the flight was in fact "safe and sound in Austria," and had his passport stolen in 2012.

Meanwhile, an Italian Foreign Ministry press office official told ABC News that no Italian was on the plane. The parents of Italian Luigi Maraldi, whose name is also on the passenger manifest, told Italian TV station RAI that their son had called them early this morning from Thailand where he is vacationing. Maraldi's passport was stolen about a year ago while he was on vacation in Thailand, his parents said.

Official sources told ABC News today they are investigating the two stolen passports and hoping that the Malaysian airport has security cameras that recorded passengers headed to the flight. Those images can be compared to various databases, provided they exist and the Malaysians will share them.

The U.S. government is also planning to review all the names of passengers and crew on the flight manifest, sources said. The names, which are available through open source, will be run through all relevant terrorism and criminal databases the government has access to. A formal request may have already been made through the TSA or State Department, one official said.

U.S. officials emphasized that there is no evidence of terrorism, but it is conducting the review to check for any potential leads. They are not ruling anything out at this stage, especially considering so few facts have been revealed in the case and no wreckage has been recovered, sources said.

Authorities volunteered tonight that stolen passports and counterfeit passports are often used for drug smuggling in that area of the world.

Meanwhile, a massive search and rescue operation is currently under way for the Boeing 777-200 aircraft, more than 24 hours after air traffic controllers lost contact with the plane.

A spokesman for Malaysia Airlines said Friday that the passengers included travelers from America, Canada, Britain, Australia, France, India, the Netherlands, Russia and several other countries.

"An international search and rescue mission from Malaysia, Singapore and Vietnam was mobilized this morning. At this stage, they have failed to find evidence of any wreckage. The sea mission will continue overnight while the air mission will recommence at daylight," Malaysia Airlines said in a statement posted on its website at 2 a.m. local time Sunday.

The three Americans on board the Malaysia Airlines flight that went missing in Southeast Asia have been identified as Philip Wood, 51; Nicolechd Meng, 4; and Yan Zhang, 2, according to the flight's manifest.